Taro (Colocasia esculenta) Transformed with a Wheat Oxalate Oxidase Gene for Improved Resistance to Taro Pathogen Phytophthora colocasiae

Production of taro [Colocasia esculenta (L.) Schott], a tropical root crop, is declining in many areas of the world as a result of the spread of diseases such as Taro leaf blight (TLB). Taro cv. Bun Long was transformed through Agrobacterium tumefaciens with the oxalate oxidase (OxO) gene gf2.8 from wheat (Triticaum aestivum). Insertion of this gene was confirmed by polymerase chain reaction (PCR) and Southern blot analysis. One independent transformed line contained one gene insertion (g5), whereas a second independent line contained four copies of the gene. Reverse transcriptase PCR (RT-PCR) confirmed the expression of this gene in line g5. Histochemical analysis of the enzyme oxalate oxidase confirmed its activity increased in the leaves of line g5. A bioassay for resistance to TLB used zoospores of Phytophthora colocasiae to inoculate tissue-cultured plantlets. Transgenic line g5 showed the complete arrest of this disease; in contrast, the pathogen killed non-transformed plants by 12 days after inoculation. A second bioassay, in which spores of P. colocasiae were inoculated onto disks of leaves of one-year-old potted plants, confirmed that transgenic line g5 had greatly increased resistance to this pathogen. This is the first report to demonstrate that genetic transformation of a crop species with an OxO gene could confer increased resistance to a pathogen (P. colocasiae) that does not secrete oxalic acid (OA).